1. Field of the Invention
The present invention relates generally to the field of torque driving tool apparatus and, more particularly, to a rotatable driving tool for imparting torque to a driven member, such as a threaded fastener. The invention also relates generally to the cooperation between the driving tool and a socket or recess in the driven member.
2. Description of the Prior Art
A typical torque driving tool apparatus includes a driving tool such as, for example, a screwdriver, which has a bit portion engageable in a complementary recess in the head of a rotatably driven member, such as a screw, bolt or the like. An area of concern in torque driving tool assemblies has been the retention of the fastener or other driven member on the bit of the driving tool. This may be important, for example, in applications where the driven member must be applied or mounted in an inaccessible location such that the only means available for delivering the fastener to the location and/or stabilizing it during the driving operation is the driving tool itself.
One type of retention technique is the use of a magnetized bit on the driving tool. This type of retention is, however, useful only with driven members which are formed of magnetic material.
One other approach has been to use a tapered bit on the driving tool which is adapted to wedge into an interference fit in the recess of the driven member. A disadvantage of such arrangements is that the bit engages the driven member only at the outer end of the recess. This results in inefficient transfer of the torque from the driving member to the driven member. Also, the concentration of force at one contact location tends to wear and deform the recess in the contact region. Furthermore, it has been found that very close tolerances are necessary in order to provide the proper wedge fit in a consistent manner.